From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 9E5E0C7EE29 for ; Fri, 2 Jun 2023 19:24:16 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S237205AbjFBTYP (ORCPT ); Fri, 2 Jun 2023 15:24:15 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:35450 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S235251AbjFBTYN (ORCPT ); Fri, 2 Jun 2023 15:24:13 -0400 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id CF3321BE for ; Fri, 2 Jun 2023 12:23:24 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1685733804; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=Hl/Yio++/nUxex1lxp6/0KZZRVMOQifT21+LBrMdJ5A=; b=dDibgMqJfHY9EacCDw9HaMdM6UMfkAAp8zCrNvBXj9IQB+EhzjdJ5IeQsYP5h29a+qqLYg 9UgRrvTZWwKyTeEgzxVVgNGRYFkRIfBNYB6Hf1n6IfvzyYzBwuHSE+uGjps+Gc9nVJw6US Cd7+Ncj1NIvl/hGEF4AtzLgAlSOcXHU= Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-136-s9DeVHr9PSiNgf7LjKdAhw-1; Fri, 02 Jun 2023 15:23:20 -0400 X-MC-Unique: s9DeVHr9PSiNgf7LjKdAhw-1 Received: from smtp.corp.redhat.com (int-mx08.intmail.prod.int.rdu2.redhat.com [10.11.54.8]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id CD4BD85A5BA; Fri, 2 Jun 2023 19:23:19 +0000 (UTC) Received: from dhcp-27-174.brq.redhat.com (unknown [10.45.224.50]) by smtp.corp.redhat.com (Postfix) with SMTP id B8E9CC154D7; Fri, 2 Jun 2023 19:23:16 +0000 (UTC) Received: by dhcp-27-174.brq.redhat.com (nbSMTP-1.00) for uid 1000 oleg@redhat.com; Fri, 2 Jun 2023 21:22:58 +0200 (CEST) Date: Fri, 2 Jun 2023 21:22:55 +0200 From: Oleg Nesterov To: Mike Christie Cc: linux@leemhuis.info, nicolas.dichtel@6wind.com, axboe@kernel.dk, ebiederm@xmission.com, torvalds@linux-foundation.org, linux-kernel@vger.kernel.org, virtualization@lists.linux-foundation.org, mst@redhat.com, sgarzare@redhat.com, jasowang@redhat.com, stefanha@redhat.com, brauner@kernel.org Subject: Re: [PATCH 1/1] fork, vhost: Use CLONE_THREAD to fix freezer/ps regression Message-ID: <20230602192254.GD555@redhat.com> References: <20230601183232.8384-1-michael.christie@oracle.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230601183232.8384-1-michael.christie@oracle.com> User-Agent: Mutt/1.5.24 (2015-08-30) X-Scanned-By: MIMEDefang 3.1 on 10.11.54.8 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Mike, sorry, but somehow I can't understand this patch... I'll try to read it with a fresh head on Weekend, but for example, On 06/01, Mike Christie wrote: > > static int vhost_task_fn(void *data) > { > struct vhost_task *vtsk = data; > - int ret; > + bool dead = false; > + > + for (;;) { > + bool did_work; > + > + /* mb paired w/ vhost_task_stop */ > + if (test_bit(VHOST_TASK_FLAGS_STOP, &vtsk->flags)) > + break; > + > + if (!dead && signal_pending(current)) { > + struct ksignal ksig; > + /* > + * Calling get_signal will block in SIGSTOP, > + * or clear fatal_signal_pending, but remember > + * what was set. > + * > + * This thread won't actually exit until all > + * of the file descriptors are closed, and > + * the release function is called. > + */ > + dead = get_signal(&ksig); > + if (dead) > + clear_thread_flag(TIF_SIGPENDING); this can't be right or I am totally confused. Another signal_wake_up() can come right after clear(SIGPENDING). Again, I'll try to re-read this patch, but let me ask anyway... Do we have a plan B? I mean... iirc you have mentioned that you can change these code paths to do something like if (killed) tell_the_drivers_that_all_callbacks_will_fail(); so that vhost_worker() can exit after get_signal() returns SIGKILL. Probably I misunderstood you, but it would be nice to avoid the changes in coredump/etc code just to add a temporary (iiuc!) fix. Oleg.